In the field of fuel cell generation systems, there are used reforming apparatuses which produce reformed gases containing hydrogen as a main component by steam-reforming a fuel gas as a raw material (e.g. alcohols such as methanol etc., hydrocarbons such as methane, buthane, etc., fossil fuels such as naphtha, LNG, etc.).
FIG. 20 shows one of the reforming apparatuses disclosed in Japanese Patent Kokai Publication No. 2001-180911. This reforming apparatus comprises a reforming reactor (46) charged with a reforming catalyst (45), a shift rector (48) charged with a shift catalyst (47), and a CO-selective oxidizing reactor (50) charged with a CO-selective oxidizing catalyst (49), which are arranged separately from one another. When a fuel gas and steam are fed to the reforming reactor (46), a hydrogen-rich reformed gas is produced from the fuel gas through the steam-reforming reaction. Since this reforming reaction is an endothermic reaction, a burner (51) for heating the reforming reactor (46) to a temperature suitable for the reforming reaction is installed. The shift reactor (48) converts the carbon monoxide in the reformed gas produced by the reforming reactor (46) to obtain hydrogen through a water gas shift reaction, to thereby reduce an amount of carbon monoxide. Since this shift reaction is an exothermic reaction, heating is unnecessary during the steady state operation, however, a burner (52) is arranged to heat the reactor to a temperature suitable for the shift reaction at the time of starting the operation. The CO-selective oxidizing reactor (50) oxidizes the carbon monoxide in the reformed gas having undergone the shift reaction into carbon dioxide through a CO-selective oxidizing reaction, and thus, an amount of carbon monoxide in the reformed gas is further reduced. By doing so, the reformed gas which is rich in hydrogen is obtained as a final product. Since the CO-selective oxidizing reaction is an exothermic reaction, heating is unnecessary during the steady operation, however, a burner (53) is arranged to heat the reactor to a temperature suitable for the CO-selective oxidizing reaction at the time of starting the operation. Further, cooling water passages (55, 56) are arranged in the shift reactor (48) and the CO-selective oxidizing reactor (50) so as to properly control the temperatures thereof.
According the reforming apparatus shown in FIG. 20, it is possible to properly control the temperatures of the respective reactors (46, 48, 50), and to produce reformed gases suitable from a variety of fuel gases for polymer electrolyte fuel cells.
However, the reforming apparatus shown in FIG. 20 has the following problems, since the reforming reactor (46), the shift reactor (48) and the CO-selective oxidizing reactor (50) are arranged separately from one another: heat release from the reactors (46, 48, 50) leads to larger heat loss, resulting in a poor heat efficiency; because of the above separate arrangement, the heating burners (51, 52, 53) must be provided on the reactors (46, 48, 50), respectively, which results in a complicated apparatus, and also requires a larger amount of energy to start the operation of the apparatus, which results in a poor starting performance.
FIG. 21 shows one of the reforming apparatuses disclosed in International Publication No. WO 00/63114. This reforming apparatus has a multi-cylindrical structure which comprises an outer cylinder (58), a group of intermediate cylinders (59) (59a to 59g) which are arranged concentrically inside the outer cylinder (58), and an inner cylinder (60) which is arranged concentrically inside the group of the intermediate cylinders (59). A reforming catalyst layer (61) fills an annular space formed between the inner cylinder (60) and the innermost intermediate cylinder (59g); a shift catalytic layer (62) fills an annular space formed between the intermediate cylinder (59d) and the intermediate cylinder (59e); and a CO-selective oxidizing catalytic layer (63) fills an annular space formed between the outermost intermediate cylinder (59a) and the intermediate cylinder (59b) on its inner side. Further, a heat-transfer partition wall (a heat-radiation cylinder) (64) is arranged concentrically inside the inner cylinder (60), and a heating burner (66) is mounted on a burner mount (65) inside the heat-transfer partition wall (64).
According to the reforming apparatus shown in FIG. 21, the heat-transfer partition wall (64) and the inner cylinder (60) which are heated by a combustion gas from the heating burner (66), the reforming catalytic layer (61) through which a fuel gas and a gas having undergone the reforming reaction are allowed to pass, and the shift catalytic layer (62) and the CO-selective oxidizing catalytic layer (63) are arranged concentric as a multi-cylindrical structure. Therefore, heat releases only from the outer cylinder (58), which results in a smaller heat loss. Thus, advantageously, the reforming apparatus can be made compact with a higher efficiency. In addition, since the reforming catalytic layer (61), the shift catalytic layer (62) and the CO-selective oxidizing catalytic layer (63) can be heated by one burner (66), the operation-starting performance of the apparatus is excellent.
However, the reforming apparatus shown in FIG. 21 has a problem in its complicated structure because of the multi-cylindrical structure comprising a number of cylinders.
FIG. 22 shows one of the reforming apparatuses disclosed in International Publication No. WO 98/00361. This reforming apparatus comprises an inner cylindrical body (70) disposed around a combustion gas passage (69) through which a combustion gas from a burner (68) passes, and an outer cylindrical body (71) disposed outside the inner cylindrical body (70), wherein the upper ends of the inner cylindrical body (70) and the outer cylindrical body (71) are communicated with each other. The inner cylinder (70) is charged with a reforming catalyst to form a reforming reaction section (72) therein, and the outer cylinder (71) is charged with a shift catalyst and a CO-selective oxidizing catalyst to form therein a shift reaction section (73) and a CO-selective oxidizing reaction section (74), respectively.
According to the reforming apparatus shown in FIG. 22, the combustion gas passage (69) through which the combustion gas from the heating burner (68) passes, and the inner cylindrical body (70) and the outer cylindrical body (71) through which a reformed gas produced by reforming a fuel gas passes are arranged concentrically, and therefore, heat is released only from the outer cylindrical body (71) to thereby lessen the heat release loss. Thus, the reforming apparatus can be made compact with a higher efficiency. In addition, the operation-starting performance of the apparatus is high because the reforming reaction section (72), the shift reaction section (73) and the CO-selective oxidizing reaction section (74) can be heated by one burner (68). Further, the apparatus is constructed by a less number of cylindrical bodies, and thus simple in its structure.
However, the reforming apparatus shown in FIG. 22 has a problem in its poor heat efficiency as follows: The relatively high temperature of the reforming reaction section (72), and the relatively low temperatures of the shift reaction section (73) and the selective oxidizing section (74) are suitably controlled, respectively, by disposing a partition portion (75) between the inner cylinder (70) and the outer cylinder (71) so as to control a quantity of transferred heat. Therefore, quantities of heat of the reformed gases in the inner cylinder (70) and the outer cylinder (71) are not sufficiently recovered and used, which results in a poor heat efficiency.